This invention relates to an internal combustion engine comprising an engine unit support which contains the engine parts directly affected by body resonance and sound vibration, namely cylinderhead, cylinder, piston, connecting rod, crankshaft main bearings, and crankshaft, and a crankcase cast integral with the flywheel housing. The crankcase is connected to the engine unit support on flanges located above the crankshaft. The crankshaft main bearings consist each of a bearing block and a bearing cap forming a main bearing unit detachably secured to the engine unit support.